Blood group M & N antigens and their immediate precursors T and Tn occur as glycoproteins in human red blood cells. Recently we found an animal adenocarcinoma in collaboration with Dr. J. L. Cantrell where these structures are confined to the glycolipid fraction. Elucidation of the structural basis for M-, N-, T- and Tn-specificities on red blood cells and on adenocarcinomata is proposed. An integral part of the overall goal of the proposed work is to establish the significance of these cell surface receptors, especially T in human (breast) adenocarcinoma, in view of the profound cellular and humoral immune response which breast carcinoma patients but not control persons show against it. Sialyltransferase studies to establish structural differences between M- and N-specific immunodeterminants will be continued. Sialyltransferase activities in the breast carcinoma tissue and in healthy glandular tissue will be compared with an aim to determine if the carcinoma-associated T- and Tn-specific structures are products of incomplete biosynthesis or accelerated degradation.